Schistosomiasis is a parasitic infection acquired by swimming, wading, bathing, or washing in fresh water that contains snails and that has been contaminated by feces or urine carrying parasite eggs from infected persons. Once in the water, the eggs hatch, releasing an immature form of the parasite that infects snails. The parasite undergoes further development in the snail, emerging in a stage that has the capacity to penetrate intact human skin. Once inside its human host, the parasite matures into an adult worm and lays eggs, which may migrate to bladder (urinary schistosomiasis) or to the intestines or liver (intestinal or hepatic schistosomiasis), depending upon the species. Early symptoms may include fever, loss of appetite, weight loss, abdominal pain, weakness, headaches, joint and muscle pains, diarrhea, nausea, and cough, but most infections are asymptomatic at first. Long-term complications may include kidney failure (urinary schistosomiasis) or malabsorption, enlargement of the liver and spleen, engorgement of the esophageal blood vessels, and accumulation of fluid in the abdominal cavity (intestinal or hepatic schistosomiasis). Occasionally, eggs may be deposited in the brain or spinal cord, leading to seizures or paralysis. The drug of choice for most forms of schistosomiasis is praziquantel. There is no vaccine at present.

Travelers to Africa, especially those who swim, wade, or raft in fresh water, are at greatest risk for schistosomiasis. A recent study from Europe found that most infections were imported from Mali, Senegal, Ghana, Democratic Republic of the Congo, and Uganda. Those traveling for missionary or volunteer work or as expatriates are at highest risk. The disease is occasionally reported after travel to Asia or South America. The key to prevention is avoiding bodies of fresh water, such as lakes, ponds, streams, and rivers, in places where schistosomiasis might occur. Salt water and chlorinated pools are thought to carry no risk of schistosomiasis. Water for bathing or showering should be heated to 150 degrees F for at least 5 minutes or held in a storage tank for at least 3 days. Toweling oneself dry after unavoidable or accidental exposure to contaminated water may reduce the likelihood of schistosomiasis, but does not reliably prevent the disease and is no substitute for the precautions above. Chlorinated swimming pools are considered safe.